Process for the preparation of polyesters and copolyesters

Abstract

The preparation of polyesters and copolyesters, titanium dioxide precipitates and/or titanium dioxide/silicon dioxide coprecipitates having a composition of TiO.sub.2 :SiO.sub.2 >90:10 mol/mol and/or titanium dioxide/zirconium dioxide coprecipitates having a composition of TiO.sub.2 :ZrO.sub.2 >95:5 mol/mol, which have been obtained by hydrolytic precipitation of the corresponding metal alcoholates formed from mono- or polyhydric alcohols, are proposed as polycondensation catalysts. They offer increased safety for the ecosystem and have a higher catalytic activity than Sb.sub.2 O.sub.3, so that the preferred amount used is only 10 to 100 ppm, based on the esters or oligoesters to be subjected to polycondensation. Their storage stability is good if the catalysts have a water content of from 0 to about 15 weight percent, preferably from 0 to about 5 weight percent based upon the hydrated precipitate or coprecipitate, as determined by Karl Fischer titration.

Claims

1. A process for the preparation of polyesters and copolyesters comprising the polycondensation of polyester-forming starting components, esters or oligoesters being prepared in a first reaction stage and subjected to polycondensation in a second reaction stage in the presence of titanium catalysts, wherein in the polycondensation stage, at least one of a titanium dioxide precipitate, a titanium dioxide/silicon dioxide coprecipitate having a composition of TiO.sub.2:SiO.sub.2 of >90:10 mol/mol and a titanium dioxide/zirconium dioxide coprecipitate having a composition of TiO.sub.2:ZrO.sub.2 of >95:5 mol/mol, which have been obtained by hydrolytic precipitation of the corresponding metal alcoholates formed from mono- or polyhydric alcohols, whereby the hydrolytic precipitation is performed by first introducing the metal alcoholate into the precipitation vessel and subsequently slowly adding the medium containing the precipitating agent water, is employed as the polycondensation catalyst for polycondensation of the esters or oligoesters.

2. The process according to claim 1, wherein the titanium dioxide precipitates, titanium dioxide/silicon dioxide coprecipitates, and titanium dioxide/zirconium dioxide coprecipitates which have been obtained by hydrolytic precipitation of the corresponding metal alcoholates formed from monohydric alcohols having 1-6C atoms are employed.

3. The process according to claim 1, wherein at least one of the titanium dioxide precipitate, the titanium dioxide/silicon dioxide coprecipitate, and the titanium dioxide/zirconium dioxide coprecipitate is employed in a total amount of 5-500 ppm, based on the esters or oligoesters to be subjected to polycondensation.

4. The process according to claim 3, wherein at least one of the titanium dioxide precipitate, the titanium dioxide/silicon dioxide coprecipitate, and the titanium dioxide/zirconium dioxide coprecipitate is employed in a total amount of 10 to 100 ppm, based on the esters or oligoesters to be subjected to polycondensation.

5. The process according claim 1, wherein at least one of the titanium dioxide precipitate, the titanium dioxide/silicon dioxide coprecipitate, and the titanium dioxide/zirconium dioxide coprecipitate is employed with a water content of from 0 to about 15 weight percent based upon the hydrated precipitate or coprecipitate.

6. The process according claim 1, wherein at least one of the titanium dioxide precipitate, the titanium dioxide/silicon dioxide coprecipitate, and the titanium dioxide/zirconium dioxide coprecipitate is added in the form of a 5 to 20% strength by weight suspension in glycol to the esters or oligoesters to be subjected to polycondensation before their polycondensation.

7. The process according to claim 1, wherein any transesterification catalysts present from the first reaction stage are blocked by additional addition of one or more phosphorus compounds.

8. The process according to claim 7, wherein carbethoxy-methyl-diethyl phosphonate, di(polyoxyethylene)hydroxy-methyl phosphonate, tetraisopropyl methylene-diphosphonate and/or H.sub.3 PO.sub.4 are employed as the blocking agent.

9. A method for using of the polycondensation catalysts according to claim 1 for the preparation of alkyd resins having a relative molecular weight of <10,000.

10. A method for using the polycondensation catalysts according to claim 1 for the preparation of saturated polyester resins having a relative molecular weight of <10,000.

11. A method for using the polycondensation catalysts according to claim 1 for the preparation of polyesters and copolyesters as precursors for polyurethanes having a relative molecular weight of <10,000.

12. A method for using the polycondensation catalysts according to claim 1 for the preparation of thermoplastic polyesters and copolyesters having a relative molecular weight of >10,000.

13. A method for using the polycondensation catalysts according to claim 12 for the preparation of polyethylene terephthalate, polybutylene terephthalate, poly(ethylene 2,6-naphthalene-dicarboxylate), poly(butylene 2,6-naphthalene-dicarboxylate), poly(1,4-dimethylenecyclohexane terephthalate) and copolyesters thereof based on high homopolyester contents of at least 80 mol per cent.

14. A method for using the polycondensation catalysts according to claim 12 for the preparation of polyether-esters.

15. A method for using the polycondensation catalysts according to claim 1 for the preparation of completely aromatic or liquid-crystalline polyesters.